Thermodynamic suppression of Brownian motion

We have used helium-3 nuclear reaction analysis to measure the Brownian mot ion (intradiffusion coefficient) of polystyrene in a partially miscible ble nd with poly( alpha -methylstyrene). In the one-phase region, when the corr elation length is close to the polystyrene chain size, the intradiffusion c oefficient falls to half of its thermal value. For larger and smaller Value s of the correlation length, diffusion is normal. These results show that t he correlation length of a polymer blend constrains polymer diffusion, as s uggested from previous neutron scattering measurements, and mean-field theo ry.